1. Field of the Invention
The present application relates to polyaniline coordinated with a transition metal and a preparation method thereof, and more particularly, to polyaniline which is coordinated with a transition metal and can be regulated in a band gap energy level, a core-shell nanoparticle including the same as a core, and preparation methods thereof.
2. Discussion of Related Art
Polyaniline has been applied to anti-corrosion materials, antistatic materials, static discharge materials, electro-magnetic interference (EMI) shielding materials, electrochromic devices, battery electrodes, semiconductors, or solar cells, and can be utilized in more various applications by improving its electrical conductivity.
Generally, polyaniline can be prepared according to roughly two methods, i.e., an electrochemical method and a chemical oxidation method that uses an oxidation-reduction reaction or an acid/base reaction. However, the chemical oxidation method is suitable for commercially producing polyaniline.
A representative chemical oxidation method for preparing polyaniline has been reported by MacDiarmid et al., and according to this method, aniline monomers dissolved in hydrochloric acid with oxidizing agents such as ammonium persulfate are polymerized in an aqueous solution and the precipitates are separated and washed. Polyaniline prepared using hydrochloric acid as a dopant as such has an electrical conductivity of about 5 S/cm. (Non-Patent Document 1).
Recently, there has been reported a preparation method of water-soluble polyaniline using a polymer with an acid group as a dopant, and the polyaniline has a low electrical conductivity of about 10−2 to 10−4 S/cm (Patent Document 1).
Meanwhile, there have been conducted various studies to improve electrical conductivities of organic conducting polymers. Generally, an electrical conductivity of a solid varies depending on a band gap between a valence band and a conduction band. As for an insulator, an energy gap between a valence band and a conduction band is high, and, thus, even if an electron is excited, it cannot go up to the valence band. However, as for a metal, there is no band gap, and, thus, an electron can freely move between the two bands. Further, if there is a band gap between them, an electron in the valence band is excited into the conduction band by thermal energy in crystal and leaves a positive hole behind the valence band. A substance having such a property refers to “semiconductor”.
Generally, an organic conducting polymer has a unique HOMO/LUMO level according to its chemical structure and size, and an energy band gap can be regulated by modifying such a chemical structure and size. Based on this fact, various studies regarding conducting polymers having a low band gap are conducted. However, an organic conducting polymer of which a band gap level can be substantially regulated with ease has not yet been developed.
Therefore, it is urgently demanded to develop doped polyaniline which can be improved in solubility and also regulated in a band gap energy level of polyaniline.